Contact structures having conductive portions in substrate in three-dimensional memory devices and methods for forming the same

ABSTRACT

Embodiments of structure and methods for forming a three-dimensional (3D) memory device are provided. In an example, a method for forming a 3D memory device includes forming a first source contact portion in a substrate, forming a dielectric stack over the first source contact portion, and forming a slit opening extending in the dielectric stack and exposing the first source contact portion. The method also includes forming a plurality of conductor layers through the slit opening and form a second source contact portion in the slit opening and in contact with the first source contact portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/739,681, filed on Jan. 10, 2020, entitled “CONTACT STRUCTURES HAVINGCONDUCTIVE PORTIONS IN SUBSTRATE IN THREE-DIMENSIONAL MEMORY DEVICES ANDMETHODS FOR FORMING THE SAME,” issued as U.S. Pat. No. 11,411,014, whichis a continuation of International Application No. PCT/CN2019/120213,filed on Nov. 22, 2019, entitled “CONTACT STRUCTURES HAVING CONDUCTIVEPORTIONS IN SUBSTRATE IN THREE-DIMENSIONAL MEMORY DEVICES AND METHODSFOR FORMING THE SAME,” both of which are hereby incorporated byreference in their entireties. This application is also related to U.S.application Ser. No. 16/739,692, filed on Jan. 10, 2020, entitled“CONTACT STRUCTURES HAVING CONDUCTIVE PORTIONS IN SUBSTRATE INTHREE-DIMENSIONAL MEMORY DEVICES AND METHODS FOR FORMING THE SAME,”issued as U.S. Pat. No. 11,195,853, which is hereby incorporated byreference in its entirety.

BACKGROUND

Embodiments of the present disclosure relate to contact structureshaving conductive portions in substrate in three-dimensional (3D) memorydevices, and methods for forming the 3D memory devices.

Planar memory cells are scaled to smaller sizes by improving processtechnology, circuit design, programming algorithm, and fabricationprocess. However, as feature sizes of the memory cells approach a lowerlimit, planar process and fabrication techniques become challenging andcostly. As a result, memory density for planar memory cells approachesan upper limit.

A 3D memory architecture can address the density limitation in planarmemory cells. 3D memory architecture includes a memory array andperipheral devices for controlling signals to and from the memory array.

SUMMARY

Embodiments of contact structures having conductive portions insubstrate in 3D memory devices and methods for forming the 3D memorydevices are provided.

In one example, a 3D memory device includes a substrate, a memory stackon the substrate; and a source contact structure extending verticallythrough the memory stack. The source contact structure includes a firstsource contact portion in the substrate and having a conductive materialdifferent from the substrate. The source contact structure also includesa second source contact portion above, in contact with, and conductivelyconnected to the first source contact portion.

In another example, a 3D memory device includes a substrate, a memorystack on the substrate, a memory string extending vertically through thememory stack a source contact extending vertically through the memorystack, and a metal layer in the substrate. The metal layer is in contactwith and conductively connected to the source contact.

In a further example, a method for forming a 3D memory device includesforming a first source contact portion in a substrate, forming adielectric stack over the first source contact portion, and forming aslit opening extending in the dielectric stack and exposing the firstsource contact portion. The method also includes forming a plurality ofconductor layers through the slit opening and form a second sourcecontact portion in the slit opening and in contact with the first sourcecontact portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosureand, together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1A illustrates a cross-sectional view of a 3D memory device havinga source contact and a peripheral contact.

FIG. 1B illustrates a top view of the 3D memory device shown in FIG. 1A.

FIG. 2A illustrates a cross-sectional view of an exemplary 3D memorydevice having a source contact structure and a peripheral contactstructure, according to some embodiments of the present disclosure.

FIG. 2B illustrates a top view of the exemplary 3D memory device shownin FIG. 2A, according to some embodiments of the present disclosure.

FIGS. 3A-3C illustrate cross-sectional views of a conductive portion atvarious stages of an exemplary fabrication process, according to someembodiments of the present disclosure.

FIGS. 4A-4C illustrate cross-sectional views of a 3D memory devicehaving a source contact structure partially in a substrate at variousstages of an exemplary fabrication process, according to someembodiments of the present disclosure.

FIGS. 5A and 5B illustrate cross-sectional views of a 3D memory devicehaving a peripheral contact structure partially in a substrate atvarious stages of an exemplary fabrication process, according to someembodiments of the present disclosure.

FIG. 6 illustrates a flowchart of an exemplary fabrication process forforming a conductive portion in a substrate, according to someembodiments of the present disclosure.

FIG. 7 illustrates a flowchart of an exemplary fabrication process forforming a 3D memory device having a source contact structure, accordingto some embodiments of the present disclosure.

FIG. 8 illustrates a flowchart of an exemplary fabrication process forforming a 3D memory device having a peripheral contact structure,according to some embodiments of the present disclosure.

Embodiments of the present disclosure will be described with referenceto the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, thisshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to affect such feature, structure orcharacteristic in connection with other embodiments whether or notexplicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context. In addition, the term “basedon” may be understood as not necessarily intended to convey an exclusiveset of factors and may, instead, allow for existence of additionalfactors not necessarily expressly described, again, depending at leastin part on context.

As used herein, the term “nominal/nominally” refers to a desired, ortarget, value of a characteristic or parameter for a component or aprocess operation, set during the design phase of a product or aprocess, together with a range of values above and/or below the desiredvalue. The range of values can be due to slight variations inmanufacturing processes or tolerances. As used herein, the term “about”indicates the value of a given quantity that can vary based on aparticular technology node associated with the subject semiconductordevice. Based on the particular technology node, the term “about” canindicate a value of a given quantity that varies within, for example,10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

As used herein, a staircase structure refers to a set of surfaces thatinclude at least two horizontal surfaces (e.g., along x-y plane) and atleast two (e.g., first and second) vertical surfaces (e.g., alongz-axis) such that each horizontal surface is adjoined to a firstvertical surface that extends upward from a first edge of the horizontalsurface, and is adjoined to a second vertical surface that extendsdownward from a second edge of the horizontal surface. A “step” or“staircase” refers to a vertical shift in the height of a set ofadjoined surfaces. In the present disclosure, the term “staircase” andthe term “step” refer to one level of a staircase structure and are usedinterchangeably. In the present disclosure, a horizontal direction canrefer to a direction (e.g., the x-axis or the y-axis) parallel with thetop surface of the substrate (e.g., the substrate that provides thefabrication platform for formation of structures over it), and avertical direction can refer to a direction (e.g., the z-axis)perpendicular to the top surface of the structure.

NAND flash memory devices, widely used in various electronic produces,are non-volatile, light-weighted, of low power consumption and goodperformance. Currently, planar NAND flash memory devices have reachedits storage limit. To further increase the storage capacity and reducethe storage cost per bit, 3D memory devices, e.g., 3D NAND memorydevices, have been proposed. An existing 3D NAND memory device oftenincludes a plurality of memory blocks. Adjacent memory blocks are oftenseparated by a gate line slit (GLS) in which an array common source(ACS) contact is formed. Peripheral contacts are formed outside of thememory blocks for transmitting electrical signals around the memoryblocks.

In the fabrication method to form existing 3D NAND memory devices, anincreased number of levels are formed vertically to obtain higherstorage capacity. The increased number of levels along the verticaldirection can result in undesirably high stress on the GLS, causingdeformation or even collapse of the GLS. The conductive materialdeposited in the GLS for forming the ACS can also impose undesirablyhigh stress on the neighboring memory blocks, causing deformation inthese regions. To reduce the susceptibility of the GLS to the highstress, connecting structures (e.g., bridges) have been formed above thesubstrate to support and/or conductively connect different portions ofthe ACS contact. However, the formation of the connecting structures canbe demanding on the precision of the fabrication process, and oftenrequires additional masks/fabrication operations, increasing theproduction cost.

In another aspect, peripheral contacts in the existing 3D NAND memorydevices are formed by the same etching process that forms the word linecontacts (e.g., the contacts that are in contact with the conductorlayers/word lines). The etching to form the PC openings (i.e., openingsfor forming the peripheral contacts) often needs to stop on thesubstrate, e.g., semiconductor such as silicon, and the etching to formthe WL openings (i.e., opening for forming the word line contacts) oftenneeds to stop on the conductor layers, e.g., metal such as tungsten.Often, the PC openings are over etched to remove a portion of thesubstrate to improve the contact between the substrate and thesubsequently-formed peripheral contacts. The over-etching and thedifferent etch-stop materials and different etching depths of the twotypes of contacts can cause the conductor layers at the bottoms of theWL openings to be undesirably etched or even punched through, resultingshort circuits. To reduce the possibility of punch-throughs in theopenings, other approaches have been introduced. For example, instead ofremoving the portion of the substrate using the same etching processthat forms the PC openings and the WL openings, the PC openings are notover etched and an additional etching process by a gas etchant isemployed to remove the portion of the substrate at the bottoms of the PCopenings. The gas etchant has a lower etch rate on the conductor layerand thus is less likely to cause punch-throughs in the conductor layers.However, the gas etchant is often erosive to the insulating material inwhich the WL openings are formed and can cause undesirable enlargementof the critical dimension (CD) of the WL openings. The performance ofthe 3D NAND memory devices can be affected.

FIG. 1A illustrates a cross-sectional view of an existing 3D NAND memorydevice 100 having a source contact and a peripheral contact. FIG. 1Billustrates a top view of 3D NAND memory device 100. As shown in FIG.1A, 3D NAND memory device 100 includes an insulating structure 116 overa substrate 102, a memory stack 104 in insulating structure 116 and overa substrate 102, a source contact 106 (e.g., ACS contact) extendingvertically through memory stack 104, and a doped region 118 in substrate102. Memory stack 104 includes interleaved a plurality of conductorlayers 112 and a plurality of insulating layers 114. 3D NAND memorydevice 100 also includes a peripheral contact 108 extending verticallythrough insulating structure 116 and in contact with substrate 102, anda word line contact 110 extending through insulating structure 116 andin contact with conductor layers 112. As shown in FIG. 1A, doped region118 is in contact with source contact 106 and substrate 102, providing aconductive connection in between. Peripheral contact 108 extends intosubstrate 102, forming conductive connection with substrate 102. Asshown in FIG. 1B, source contact 106 extends laterally in memory stack104, dividing memory cells in memory stack 104 into a plurality offingers. Peripheral contacts 108 are located outside of memory stack104.

The present disclosure provides a 3D memory device (e.g., 3D NAND memorydevice) having conductive portions formed in the substrate to solve theaforementioned issues in existing 3D memory devices. The conductiveportions may be referred to as being formed in a “zero layer.” Theconductive portions may include a suitable conductive material such astungsten, cobalt, copper, aluminum, silicides, and/or polysilicon. Insome embodiments, the conductive portions include tungsten. In someembodiments, a conductive portion may be a part (e.g., a first sourcecontact portion) of a source contact structure, which also has anotherpart (e.g., a second source contact portion) above and in contact withthe conductive portion. The conductive portion may extend continuouslyin the substrate, while the upper portion of the source contactstructure may include a plurality of disconnected sub-source contacts.The conductive portion may be in contact with and conductively connectedto the disconnected sub-source contacts, allowing the disconnectedsub-source contacts to be conductively connected without any connectingstructures being formed above the substrate. The stress imposed by thesource contact structure can thus be reduced by the formation of thesub-source contacts and the fabrication process of the 3D memory devicecan be simplified. In some embodiments, the conductive portion improvesthe conductivity (e.g., reduces resistance) between the second sourcecontact portion and the substrate compared to a doped region in existing3D NAND memory device (e.g., doped region 118 in 3D NAND memory device100).

In some embodiments, a conductive portion may be a part (e.g., a firstperipheral contact portion) of a peripheral contact structure, whichalso has another part (e.g., a second peripheral contact portion) aboveand in contact with the conductive portion. The conductive portion mayextend in the substrate and in contact with the substrate and/or anyother peripheral contact structures. In this example, the PC openings donot need to be over etched for forming the contact between theperipheral contact structures and the substrate, while the contact areabetween each peripheral contact structure and the substrate can beincreased. Desirably low contact resistance can be obtained between thesubstrate and the peripheral contact structures. The CD of word linecontacts can be maintained. The performance of the 3D memory device canthus be improved and the fabrication process can be simplified. In someembodiments, the conductive portions for forming the source contactstructures and the peripheral contact structures are formed in the samefabrication operations, further simplifying the fabrication process ofthe 3D memory device.

FIGS. 2A and 2B illustrate views of an exemplary 3D memory device 200having a source contact structure and a peripheral contact structure,each having a conductive portion in the substrate, according to someembodiments. Specifically, FIG. 2A illustrates a cross-sectional view of3D memory device 200 along the x-z plane, and FIG. 2B illustrates a topview of 3D memory device 200 along the x-y plane. As shown in FIG. 2A,3D memory device 200 may include a substrate 202 and a memory stack 204over substrate 202. Memory stack 204 may include interleaved a pluralityof conductor layers 212 and a plurality of dielectric layers 214. 3Dmemory device 200 may also include an insulating structure 216 in whichmemory stack 204 is located. 3D memory device 200 may further includeone or more channel structures 222 each extending vertically throughmemory stack 204 (e.g., along the z-axis), one or more source contactstructures 206 each extending vertically through memory stack 204, oneor more peripheral contact structures 208 each extending verticallythrough insulating structure 216, and one or more word line contacts 210each extending vertically in insulating structure 216 and in contact ofa respective conductor layer 212. In some embodiments, source contactstructure 206 each include a first source contact portion 206-1 embeddedin substrate 202 and a second source contact portion 206-2 above, incontact with, and conductively connected to first source contact portion206-1. In some embodiments, peripheral contact structure 208 includes afirst peripheral contact portion 208-1 embedded in substrate 202 and asecond peripheral contact portion 208-2 above, in contact with, andconductively connected to first peripheral contact portion 208-1.

Substrate 202 can include silicon (e.g., single crystalline silicon),silicon germanium (SiGe), gallium arsenide (GaAs), germanium (Ge),silicon on insulator (SOI), germanium on insulator (GOI), or any othersuitable materials. In some embodiments, substrate 202 is a thinnedsubstrate (e.g., a semiconductor layer), which was thinned by grinding,etching, chemical mechanical polishing (CMP), or any combinationthereof. In some embodiments, substrate 202 includes silicon.

Memory stack 204 may include a plurality of interleaved conductor layers212 and dielectric layers 214. The intersection of channel structures222 and conductor layers 212 may form a plurality of memory cells, e.g.,an array of memory cells, in 3D memory device 200. The number of theconductor/dielectric layer pairs in memory stack 204 (e.g., 32, 64, 96,or 128) determines the number of memory cells in 3D memory device 200.Conductor layers 212 and dielectric layers 214 may alternate in thevertical direction (e.g., the z-direction). In other words, except forthe ones at the top or bottom of memory stack 204, each conductor layer212 can be adjoined by two dielectric layers 214 on both sides, and eachdielectric layer 214 can be adjoined by two conductor layers 212 on bothsides. Conductor layers 212 can each have the same thickness or havedifferent thicknesses. Similarly, dielectric layers 214 can each havethe same thickness or have different thicknesses. Each word line contact210 may extend in insulating structure 216 and be in contact with therespective conductor layer 212, conductively connecting conductor layer212 with, e.g., a peripheral circuit. Conductor layers 212 and word linecontacts 210 can each include conductor materials including, but notlimited to, tungsten (W), cobalt (Co), copper (Cu), aluminum (Al),polycrystalline silicon (polysilicon), doped silicon, silicides, or anycombination thereof. Dielectric layers 214 can include dielectricmaterials including, but not limited to, silicon oxide, silicon nitride,silicon oxynitride, or any combination thereof. In some embodiments,conductor layers 212 include metal layers, such as W, and dielectriclayers 214 include silicon oxide.

Channel structures 222 may form an array and may each extend verticallyabove substrate 202. Channel structure 222 can include a semiconductorchannel extending vertically through the alternatingconductor/dielectric stack. Channel structure 222 can include a channelhole filled with a channel-forming structure of a plurality ofchannel-forming layers, e.g., dielectric materials (e.g., as a memoryfilm) and semiconductor materials (e.g., as a semiconductor layer). Insome embodiments, the memory film is a composite layer including atunneling layer, a memory layer (also known as a “charge trap layer”),and a blocking layer. The remaining space of the channel hole can bepartially or fully filled with a dielectric core including dielectricmaterials, such as silicon oxide. Channel structure 222 can have acylindrical shape (e.g., a pillar shape) or a trapezoid shape throughmemory stack 204. The dielectric core, semiconductor layer, thetunneling layer, the memory layer, and the blocking layer are arrangedradially from the center toward the sidewall in this order, according tosome embodiments. The semiconductor layer can include silicon, such asamorphous silicon, polysilicon, and/or single crystalline silicon. Thetunneling layer can include silicon oxide, silicon oxynitride, or anycombination thereof. The memory layer can include silicon nitride,silicon oxynitride, silicon, or any combination thereof. The blockinglayer can include silicon oxide, silicon oxynitride, high dielectricconstant (high-k) dielectrics, or any combination thereof. In oneexample, the memory layer can include a composite layer of siliconoxide/silicon oxynitride (or silicon nitride)/silicon oxide (ONO).

In some embodiments, channel structure 222 further includes a conductiveplug (e.g., a semiconductor plug) in the lower portion (e.g., at thelower end of) of channel structure 222. As used herein, the “upper end”of a component (e.g., channel structure 222) is the end farther awayfrom substrate 202 in the vertical direction, and the “lower end” of thecomponent (e.g., channel structure 222) is the end closer to substrate202 in the vertical direction when substrate 202 is positioned in thelowest plane of 3D memory device 200. The conductive plug can include asemiconductor material, such as silicon, which is epitaxially grown(e.g., using selective epitaxial growth) from substrate 202 or depositedonto substrate 202 in any suitable directions. It is understood that insome embodiments, the conductive plug includes single crystallinesilicon, the same material as substrate 202. In other words, theconductive plug can include an epitaxially-grown semiconductor layergrown from substrate 202. The conductive plug can also include adifferent material than substrate 202. In some embodiments, theconductive plug includes at least one of silicon, germanium, and silicongermanium. In some embodiments, part of the conductive plug is above thetop surface of substrate 202 and in contact with the semiconductorchannel. The conductive plug may be conductively connected to thesemiconductor channel. In some embodiments, a top surface of theconductive plug is located between a top surface and a bottom surface ofa bottom dielectric layer 214 (e.g., the dielectric layer at the bottomof memory stack 204).

In some embodiments, channel structure 222 further includes a drainstructure (e.g., channel plug) in the upper portion (e.g., at the upperend) of channel structure 222. The drain structure can be in contactwith the upper end of the semiconductor channel and may be conductivelyconnected to the semiconductor channel. The drain structure can includesemiconductor materials (e.g., polysilicon) or conductive materials(e.g., metals). In some embodiments, the drain structure includes anopening filled with Ti/TiN or Ta/TaN as an adhesion layer and tungstenas a conductor material. By covering the upper end of the semiconductorchannel during the fabrication of 3D memory device 200, the drainstructure can function as an etch stop layer to prevent etching ofdielectrics filled in the semiconductor channel, such as silicon oxideand silicon nitride.

In some embodiments, source contact structure 206 extends verticallythrough memory stack 104 and is in contact with substrate 202. In someembodiments, first source contact portion 206-1 may be embedded insubstrate 202 and second source contact portion 206-2 may be above, incontact with, and conductively connected to first source contact portion206-1. Specifically, a bottom surface of first source contact portion206-1 is below the top surface of substrate 202 and a top surface offirst source contact portion 206-1 is coplanar with the top surface ofsubstrate 202. As shown in FIG. 2A, second source contact portion 206-2may be in contact with first source contact portion 206-1 at aninterface (or the top surface of first source contact portion 206-1)that is coplanar with the top surface of substrate 202.

FIG. 2B illustrates a layout of source contact structures 206 in memorystack 204. As shown in FIG. 2B, source contact structures 206 may extendlaterally in memory stack 204, e.g., along the y-axis, dividing memorycells in memory stack 204 into a plurality of fingers. A plurality ofchannel structures 222 may be distributed in each finger. Specifically,for each source contact structure 206, first source contact portion206-1 may extend continuously along the lateral direction (e.g.,they-axis). Along the lateral direction (e.g., y-axis), a length offirst source contact portion 206-1 may be nominally equal to a length ofsecond source contact portion 206-2. In some embodiments, first sourcecontact portion 206-1 includes a conductive material such as tungsten,cobalt, aluminum, copper, silicides, polysilicon, or any combinationthereof. In some embodiments, first source contact portion 206-1includes an adhesive layer, e.g., Ti/TiN and/or Ta/TaN between theconductive material and substrate 202. Along the x-axis, a lateral widthof first source contact portion 206-1 may be equal to or greater than alateral width of second source contact portion 206-2. In someembodiments, the lateral width of first source contact portion 206-1(e.g., along the x-axis) is unchanged as first source contact portion206-1 extends along they-axis.

Referring back to FIG. 2A, second source contact portion 206-2 mayinclude an insulating spacer 207-1 and a contact 207-2 in insulatingspacer 207-1. Contact 207-2 may be in contact with and conductivelyconnected to first source contact portion 206-1, e.g., the conductivematerial of first source contact portion 206-1 such that a sourcevoltage can be applied to the memory cells through first and secondsource contact portions 206-1 and 206-2. Referring back to FIG. 2B,contact 207-2 may include a plurality of disconnected sub-contacts207-20, each being disconnected from one another (e.g., by insulatingspacers 207-1) along the y-axis. In some embodiments, each sub-contact207-20 is in contact with and conductively connected to first sourcecontact portions 206-1, e.g., the conductive material of first sourcecontact portion 206-1. In some embodiments, because contact 207-2 isdivided into a plurality of sub-contacts 207-20, each of which having alength (e.g., along the y-axis) less than the total length of secondsource contact portion 206-2 (or an existing source contact 106), thestress caused by the conductive material in each sub-contact 207-20 canbe reduced in 3D memory device 200. 3D memory device 200 is then lesssusceptible to deformation caused by the deposition of conductivematerials.

Insulating spacer 207-1 may include a dielectric material such assilicon oxide, silicon nitride, and/or silicon oxynitride. Contact 207-2may include a conductive material such as tungsten, cobalt, aluminum,copper, silicides, polysilicon, or any combination thereof. In someembodiments, the conductive material(s) in first and second sourcecontact portions 206-1 and 206-2 may be the same or different. In someembodiments, first source contact portion 206-1 includes a metal (e.g.,tungsten). In some embodiments, second source contact portion 206-2 (orcontact 207-2) includes polysilicon and a metal (e.g., tungsten) overthe polysilicon, where the polysilicon is in contact with the conductivematerial (e.g., tungsten) in first source contact portion 206-1.

Referring back to FIG. 2A, 3D memory device 200 also includes one ormore peripheral contact structures 208 extending vertically throughinsulating structure 216 and in contact with substrate 202. Peripheralcontact structure 208 may be conductively connected to substrate 202 anda peripheral circuit (not shown) for applying a voltage on substrate202. Peripheral contact structure 208 may include a first peripheralcontact portion 208-1 embedded in substrate 202 and a second peripheralcontact portion 208-2 above, in contact with, and conductively connectedto first peripheral contact portion 208-1. Specifically, a bottomsurface of first peripheral contact portion 208-1 is below the topsurface of substrate 202 and a top surface of first peripheral contactportion 208-1 is coplanar with the top surface of substrate 202. Asshown in FIG. 2A, second peripheral contact portion 208-2 may be incontact with first peripheral contact portion 208-1 at an interface (orthe top surface of first peripheral contact portion 208-1) that iscoplanar with the top surface of substrate 202.

FIG. 2B illustrates a layout of peripheral contact structures 208 inmemory stack 204. As shown in FIG. 2B, peripheral contact structures 208may be distributed outside of memory stack 204, e.g., along the x-axisand/or the y-axis, and in contact with substrate 202. Examples ofperipheral contact structure 208 may include a through-array-contact(TAC), a contact of peripheral circuits/devices, or any suitable contactthat meets the description of (i) being distributed outside of memorystack 204 and (ii) being in contact with substrate 202. One firstperipheral contact portion 208-1 may be separated/insulated from otherfirst peripheral contact portions 208-1, or in contact with andconductively connected to another first peripheral contact portion208-1, depending on the design of 3D memory device 200. The shaded areain FIG. 2B is for illustrating the distribution of first peripheralcontact portions 208-1 only and is not meant to indicate the shape,dimensions, or conductive connection of first peripheral contactportions 208-1. In some embodiments, a dimension (e.g., length or width)of first peripheral contact portion 208-1 may be equal to or greaterthan the dimension (e.g., length or width) of the respective secondperipheral contact portion 208-2 along the same lateral direction. Forexample, the length/width of first peripheral contact portion 208-1 maybe at least the same as the length/width of the respective secondperipheral contact portion 208-2 along the x-axis. In some embodiments,the lateral cross-sectional area of first peripheral contact portion208-1 (e.g., along the x-y plane) is equal to or greater than thelateral cross-sectional area of the respective second peripheral contactportion 208-2 (e.g., along the x-y plane). In some embodiments, firstperipheral contact portion 208-1 includes a conductive material such astungsten, cobalt, aluminum, copper, silicides, polysilicon, or anycombination thereof. In some embodiments, first peripheral contactportion 208-1 includes an adhesive layer, e.g., Ti/TiN and/or Ta/TaNbetween the conductive material and substrate 202.

In some embodiments, second peripheral contact portion 208-2 includes aconductive material, which can be the same as or different from theconductive material in the respective first peripheral contact portion208-1. For example, second peripheral contact portion 208-2 can includetungsten, cobalt, aluminum, copper, silicides, polysilicon, or anycombination thereof. In some embodiments, second peripheral contactportion 208-2 and the respective first peripheral contact portion 208-1include the same conductive material, e.g., tungsten. In someembodiments, second peripheral contact portion 208-2 further includes anadhesion layer e.g., Ti/TiN and/or Ta/TaN between the conductivematerial and insulating structure 216. The adhesion layer may surroundthe conductive material in second peripheral contact portion 208-2 andbe in contact with the conductive material in first peripheral contactportion 208-1.

In some embodiments, first source contact portion 206-1 and firstperipheral contact portion 208-1 each include a metal material, such astungsten. First source contact portion 206-1 and first peripheralcontact portion 208-1 may thus each be referred to as a “metal layer.”Second source contact portion 206-2 may also be described as a sourcecontact and second peripheral contact portion 208-2 may also bedescribed as a peripheral contact. Accordingly, source contact structure206 may be equivalent to a source contact in contact with a respectivemetal layer, and peripheral contact structure 208 may be equivalent to aperipheral contact in contact with a respective metal layer.

It should be noted that, for ease of illustration, source contactstructure and peripheral contact structure each having a first contactportion (e.g., conductive portion) in the substrate are illustrated inthe same figures, e.g., FIGS. 2A and 2B. In various embodiments, thesource contact structure and the peripheral contact structure may not beformed in the same 3D memory device. Also, other structures, such ascontact structures, that are conductively connected to the substrate mayalso be formed to include a conductive portion in the substrate asdescribed above, when applicable. The specific type of structure thatincludes a conductive portion in the substrate, e.g., to provide aconductive connection between the structure and the substrate, shouldnot be limited by the embodiments of the present disclosure.

FIGS. 3A-3C illustrate cross-sectional views of a 3D memory device atvarious stages of an exemplary fabrication method 300 for forming aconductive portion in a substrate, according to some embodiments. Theconductive portion may include or be employed as a first source contactportion or a first peripheral contact portion described in FIGS. 2A and2B. FIG. 6 illustrates a flowchart 600 of method 300, according to someembodiments. It is understood that the operations shown in method 300are not exhaustive and that other operations can be performed as wellbefore, after, or between any of the illustrated operations. Further,some of the operations may be performed simultaneously, or in adifferent order than shown in FIGS. 3 and 6 . Method 300 may also beemployed to form other contact portions in the substrate (if any).

At the beginning of the process, a contact pattern is formed in asubstrate (Operation 602). FIG. 3A illustrates a correspondingstructure.

As shown in FIG. 3A, a contact pattern 304 may be formed in a substrate302. In some embodiments, contact pattern 304 includes a source contactpattern and/or a peripheral contact pattern. A source contact patternmay extend continuously along a lateral direction, e.g., the y-axis, andhave a length of a respective source contact structure (e.g., sourcecontact structure 206). The peripheral contact pattern may extendcontinuously in an area in which one or more peripheral contactstructures are to be formed and conductively connected. For example, theperipheral contact pattern may extend continuously along one or morelateral directions (e.g., the x-axis and/or the y-axis). The sourcecontact pattern and the peripheral contact pattern (and other contactpatterns) may be formed separately or simultaneously. In someembodiments, the source contact pattern and the peripheral contactpattern (and any other contact patterns) are formed by the samepatterning process.

Contact pattern 304 may be formed by patterning substrate 302 using anetch mask and an etching process. For example, a patterned photoresistlayer may be formed over substrate 302, exposing portions of substrate302 corresponding to the source contact pattern and/or the peripheralcontact pattern. A suitable etching process such as anisotropic etchingprocess (e.g., dry etch) and/or isotropic etching process (e.g., wetetch) can be performed to remove the exposed portions of substrate 302,forming contact pattern 304. A bottom surface of contact pattern 304 maybe below the top surface of substrate 302.

Referring back to FIG. 6 , after the formation of the contact pattern,method 300 proceeds to Operation 604, in which a conductive material isdeposited to fill up the contact pattern. FIG. 3B illustrates acorresponding structure.

As shown in FIG. 3B, a conductive material 306 is deposited to fill upcontact pattern 304. In some embodiments, an adhesive layer 308 isdeposited over the sidewall of contact pattern 304 (e.g., the sidewallof the source contact pattern and/or the sidewall of the peripheralcontact pattern). In some embodiments, conductive material 306 includestungsten, and adhesive layer 308 includes TiN. The deposition ofconductive material 306 and adhesive layer 308 may each include ALD,CVD, and/or PVD.

Referring back to FIG. 6 , after the deposition of the conductivematerial, method 300 proceeds to Operation 606, in which the conductivematerial is planarized to form a conductive portion. FIG. 3C illustratesa corresponding structure.

As shown in FIG. 3C, conductive material 306 and any adhesive layer 308are planarized. A conductive portion 310 is formed from the planarizedconductive material 306. The planarized conductive portion 310 and anyadhesive layer 308, may include a first source contact portion (e.g.,206-1) and/or a first peripheral contact portion (e.g., 208-1).Conductive portion 310 may also include other contact portions, if any.The planarization process may include CMP and/or recess etch (e.g., dryetch and/or wet etch).

FIGS. 4A-4C illustrate cross-sectional views of a 3D memory device atvarious stages of an exemplary fabrication method 400 for forming asource contact structure, according to some embodiments. The sourcecontact structure may be similar to or the same as source contactstructure 206 described in FIGS. 2A and 2B. FIG. 7 illustrates aflowchart 700 of method 400, according to some embodiments. It isunderstood that the operations shown in method 400 are not exhaustiveand that other operations can be performed as well before, after, orbetween any of the illustrated operations. Further, some of theoperations may be performed simultaneously, or in a different order thanshown in FIGS. 4 and 7 .

At the beginning of the process, a first source contact portion isformed in a substrate (Operation 702). FIG. 4A illustrates acorresponding structure.

As shown in FIG. 4A, a first source contact portion 410-1 may be formedin a substrate 402. The description of the formation of first sourcecontact portion 410-1 can be referred to the description of theconductive portion illustrated in FIGS. 3A-3C, and the detaileddescription is not repeated herein.

Referring back to FIG. 7 , after the formation of the first sourcecontact portion, method 300 proceeds to Operation 704, in which adielectric stack is formed over the first source contact portion. FIG.4A illustrates a corresponding structure.

As shown in FIG. 4A, a dielectric stack 408 may be formed over substrate402, covering first source contact portion 410-1. As shown in FIG. 4A,dielectric stack 408 may be formed over substrate 402 by alternatinglydepositing sacrificial layers 404 and dielectric layers 406 oversubstrate 402. Sacrificial layers 404 and dielectric layers 406 may havedifferent etching selectivities during the subsequent gate-replacementprocess. In some embodiments, sacrificial layers 404 and dielectriclayers 406 include different materials. In some embodiments, sacrificiallayers 404 include silicon nitride and dielectric layers 406 includesilicon oxide. The deposition of sacrificial layers 404 and dielectriclayers 406 may each include one or more of CVD, PVD, and ALD.

In some embodiments, dielectric stack 408 may have a staircasestructure, e.g., in the staircase region of dielectric stack 408. Thestaircase structure can be formed by repetitively etching the pluralityof interleaved sacrificial layers 404 and dielectric layers 406 using anetch mask, e.g., a patterned PR layer over dielectric stack 408. Eachsacrificial layer 404 and the underlying dielectric layer 406 may bereferred to as a dielectric pair. In some embodiments, one or moredielectric pairs can form one level/stair. During the formation of thestaircase structure, the PR layer is trimmed (e.g., etched incrementallyand inwardly from the boundary of the memory stack, often from alldirections) and used as the etch mask for etching the exposed portion ofdielectric stack 408. The amount of trimmed PR can be directly related(e.g., determinant) to the dimensions of the staircases. The trimming ofthe PR layer can be obtained using a suitable etch, e.g., an isotropicdry etch such as a wet etch. One or more PR layers can be formed andtrimmed consecutively for the formation of the staircase structure. Eachdielectric pair can be etched, after the trimming of the PR layer, usingsuitable etchants to remove a portion of both sacrificial layer 404 andthe underlying dielectric layer 406. The etched sacrificial layers 404and dielectric layers 406 may form stairs in dielectric stack 408. ThePR layer can then be removed.

Referring back to FIG. 7 , after the formation of the dielectric stack,method 300 proceeds to Operation 706, in which a slit opening is formedextending in the dielectric stack and exposing the first source contactportion. FIG. 4A illustrates a corresponding structure.

As shown in FIG. 4A, a slit opening 412 is formed in dielectric stack408. Slit opening 412 may expose first source contact portion 410-1. Insome embodiments, slit opening 412 may extend continuously along thelateral direction first source contact portion 410-1 extends, e.g., they-axis. In some embodiments, along the x-axis, a lateral dimension ofslit opening 412 is less than or equal to a lateral dimension of firstsource contact portion 410-1. In some embodiments, slit opening 412 isformed by patterning dielectric stack 408 using an etch mask (e.g., apatterned photoresist layer) and a suitable etching process (e.g., dryetch).

Referring back to FIG. 7 , after the formation of the slit opening,method 300 proceeds to Operations 708 and 710, in which the sacrificiallayers in the dielectric stack are removed to form a plurality oflateral recesses and a plurality of conductor layers are formed in thelateral recesses. FIG. 4B illustrates a corresponding structure.

As shown in FIG. 4B, a plurality of conductor layers 414 are formed inthe lateral recesses through slit opening 412. In some embodiments,sacrificial layers 404 in contact with slit opening 412 are removedthrough slit opening. The removal of sacrificial layers 404 may includean isotropic etching process, e.g., wet etch. A plurality of lateralrecesses may be formed in dielectric stack 408, according to operation708. Further, according to operation 710, a conductor material may thenbe deposited to fill in the lateral recesses, forming a plurality ofconductor layers 414 in dielectric stack 408. In some embodiments, theconductor material is deposited by at least one of CVD, PVD, and ALD.Conductor layers 414 and dielectric layers 406 may be arrangedalternatingly along the z-axis above substrate 402, and a memory stack418 may be formed from dielectric stack 408.

Referring back to FIG. 7 , after the formation of the conductor layers,method 300 proceeds to Operation 712, in which a second contact portionis formed in the slit opening in contact with the first source contactportion. FIG. 4C illustrates a corresponding structure.

As shown in FIG. 4C, a second source contact portion 410-2 may be formedin slit opening 412. Second source contact portion 410-2 may be incontact with and conductively connected to first source contact portion410-1. In some embodiments, second source contact portion 410-2 includesan insulating spacer 424 and a contact 420 in insulating spacer 424. Insome embodiments, contact 420 includes a single conductive material suchas tungsten. In some embodiments, contact 420 may include a lowerportion 420-1 and an upper portion 420-2 over lower portion 420-1, eachhaving a different conductive material. In some embodiments, lowerportion 420-1 includes polysilicon and upper portion 420-2 includestungsten.

In some embodiments, contact 420 includes a plurality of sub-contactsdisconnected from one another along the direction it extends (e.g., they-axis). In some embodiments, each sub-contact is insulated from oneanother by insulating spacer 424. Contact 420 and insulating spacer 424may be formed in various ways. In some embodiments, insulating spacer424 is formed by depositing a suitable dielectric material, such assilicon oxide, in slit opening 412 to divide slit opening 412 into aplurality of slit portions along the y-axis. Insulating spacer 424 maycover the sidewall of slit opening 412 and expose first source contactportion 410-1. In an example, the dielectric material is deposited tofill up slit opening 412 and subsequently patterned, e.g., using apatterning process, to remove portions of the dielectric material andform the slit portions. One or more conductive materials may bedeposited, e.g., sequentially, to form contact 420 (or thesub-contacts). Second source contact portion 410-2 may then be formed incontact with first source contact portion 410-1, forming source contactstructure 410.

In some embodiments, the dielectric material is deposited to cover thesidewall of slit opening 412, and a recess etching process is performedto remove a portion of the dielectric material at the bottom of slitopening 412 to expose substrate 402. One or more conductive materialsmay be deposited, e.g., sequentially, into slit opening 412 to fill upthe space surrounded by the dielectric material. In some embodiments,the deposited conductive material(s) and dielectric material may then bepatterned to form one or more openings along the y-axis, separating theconductive material(s) into a plurality of sub-contacts. A suitableinsulating material, e.g., the dielectric material, may then bedeposited to fill up the openings and insulate the sub-contacts from oneanother. Second source contact portion 410-2 may then be formed incontact with first source contact portion 410-1, forming source contactstructure 410.

In various embodiments, the depositions of the conductive materialsinclude CVD, PVD, and/or ALD, and the depositions of the dielectricmaterial includes CVD, PVD, and/or ALD. The patterning of the dielectricmaterial may include a suitable etching process such as a dry etchingprocess and/or a wet etching process. The recess etch of the dielectricmaterial may include a suitable etching process such as a dry etchingprocess and/or a wet etching process. In some embodiments, aplanarization process, e.g., CMP and/or recess etch, is performed on thetop surface of memory stack 418 to remove any excess materials, e.g.,from the depositions of the conductive materials and the dielectricmaterial.

FIGS. 5A-5B illustrate cross-sectional views of a 3D memory device atvarious stages of an exemplary fabrication method 500 for forming aperipheral contact structure, according to some embodiments. Theperipheral contact structure may be similar to or the same as peripheralcontact structure 208 described in FIGS. 2A and 2B. FIG. 8 illustrates aflowchart 800 of method 500, according to some embodiments. It isunderstood that the operations shown in method 500 are not exhaustiveand that other operations can be performed as well before, after, orbetween any of the illustrated operations. Further, some of theoperations may be performed simultaneously, or in a different order thanshown in FIGS. 5 and 8 .

At the beginning of the process, a first peripheral contact portion isformed in a substrate (Operation 802). FIG. 5A illustrates acorresponding structure.

As shown in FIG. 5A, a first peripheral contact portion 510-1 may beformed in substrate 402. The description of the formation of firstperipheral contact portion 510-1 can be referred to the description ofthe conductive portion illustrated in FIGS. 3A-3C, and the detaileddescription is not repeated herein.

Referring back to FIG. 8 , after the formation of the first peripheralcontact portion 510-1, method 500 proceeds to Operation 804, in which aninsulating structure is formed over the first peripheral contactportion. FIG. 5A illustrates a corresponding structure.

As shown in FIG. 5A, an insulating structure 504 may be formed overfirst peripheral contact portion 510-1. In some embodiments, insulatingstructure 504 is deposited after the formation of the staircasestructure in the respective dielectric stack (e.g., dielectric stack408). Insulating structure 504 may surround the dielectric stack suchthat the dielectric stack is in insulating structure 504. In someembodiments, insulating structure 504 includes silicon oxide and isdeposited by ALD, CVD, and/or PVD.

Referring back to FIG. 8 , after the formation of the insulatingstructure, method 500 proceeds to Operation 806, in which an opening isformed extending in the insulating structure and exposing the firstperipheral contact portion. FIG. 5A illustrates a correspondingstructure.

As shown in FIG. 5A, an opening 512 may be formed in insulatingstructure 504. Opening 512 may extend vertically in insulating structure504 and exposing first peripheral contact portion 510-1. In someembodiments, a lateral dimension of opening 512 (e.g., along the x-axisand/or they-axis) is less than or equal to a lateral dimension of firstperipheral contact portion 510-1 along the same lateral direction(s). Insome embodiments, opening 512 is formed by a suitable etching processsuch as dry etch and/or wet etch.

Referring back to FIG. 8 , after the formation of the opening, method500 proceeds to Operation 808, in which a second peripheral contactportion is formed in the opening and in contact with the firstperipheral contact portion. FIG. 8B illustrates a correspondingstructure.

As shown in FIG. 5B, a second peripheral contact portion 510-2 is formedin opening 512. In some embodiments, an adhesive layer, e.g., TiN, isdeposited along the sidewall and the bottom surface of opening 512. Insome embodiments, the adhesive layer may be in contact with firstperipheral contact portion 510-1 (e.g., the conductive material of firstperipheral contact portion 510-1). Further, a conductive material, e.g.,tungsten, is deposited to fill up opening 512. The conductive materialand the adhesive layer (if any) may form second peripheral contactportion 510-2. A peripheral contact structure 510, having firstperipheral contact portion 510-1 and second peripheral contact portion510-2 in contact and conductively connected with each other, may beformed.

According to embodiments of the present disclosure, a 3D memory deviceincludes a substrate, a memory stack on the substrate; and a sourcecontact structure extending vertically through the memory stack. Thesource contact structure includes a first source contact portion in thesubstrate and having a conductive material different from the substrate.The source contact structure also includes a second source contactportion above, in contact with, and conductively connected to the firstsource contact portion.

In some embodiments, a bottom surface of the first source contactportion is below a top surface of the substrate and a top surface of thefirst source contact portion is coplanar with the top surface of thesubstrate.

In some embodiments, the first source contact portion includes a firstconductive material that comprises at least one of tungsten, cobalt,aluminum, copper, silicides, or polysilicon.

In some embodiments, the first source contact portion further includesan adhesive layer between the substrate and the first conductivematerial.

In some embodiments, the first source contact portion extendscontinuously along a lateral direction the source contact structureextends.

In some embodiments, the second source contact portion includes at leasttwo sub-contacts disconnected from each other along the lateraldirection.

In some embodiments, a lateral dimension of the first source contactportion is greater than a lateral dimension of the second source contactportion along a second lateral direction perpendicular to the lateraldirection.

In some embodiments, the lateral dimension of the first source contactportion is unchanged along the lateral direction.

In some embodiments, the second source contact portion includes a secondconductive material in contact with the first conductive material of thefirst source contact portion at an interface coplanar with the topsurface of the substrate.

In some embodiments, the second conductive material is different fromthe first conductive material and includes at least one of tungsten,cobalt, aluminum, copper, silicides, or polysilicon.

In some embodiments, the second source contact portion includes thefirst conductive material above and in contact with the secondconductive material.

In some embodiments, the memory stack includes interleaved a pluralityof conductor layers and a plurality of dielectric layers.

According to embodiments of the present disclosure, a 3D memory deviceincludes a substrate, a memory stack on the substrate, a memory stringextending vertically through the memory stack a source contact extendingvertically through the memory stack, and a metal layer in the substrate.The metal layer is in contact with and conductively connected to thesource contact.

In some embodiments, a bottom surface of the metal layer is below a topsurface of the substrate and a top surface of the metal layer iscoplanar with the top surface of the substrate.

In some embodiments, the metal layer includes a first conductivematerial that includes at least one of tungsten, cobalt, aluminum,copper, silicides, or polysilicon.

In some embodiments, the 3D memory device further includes an adhesivelayer between the substrate and metal layer.

In some embodiments, the metal layer extends continuously along alateral direction the source contact extends.

In some embodiments, the source contact includes at least twosub-contacts disconnected from each other along the lateral direction.

In some embodiments, a lateral dimension of the metal layer is greaterthan a lateral dimension of the source contact along a second lateraldirection perpendicular to the lateral direction.

In some embodiments, the lateral dimension of the metal layer isunchanged along the lateral direction.

In some embodiments, the source contact includes a second conductivematerial in contact with the metal layer at an interface coplanar withthe top surface of the substrate.

In some embodiments, the second conductive material is different fromthe first conductive material and includes at least one of tungsten,cobalt, aluminum, copper, silicides, or polysilicon.

In some embodiments, the source contact includes the first conductivematerial above and in contact with the second conductive material.

In some embodiments, the memory stack includes interleaved a pluralityof conductor layers and a plurality of dielectric layers.

According to embodiments of the present disclosure, a method for forminga 3D memory device includes forming a first source contact portion in asubstrate, forming a dielectric stack over the first source contactportion, and forming a slit opening extending in the dielectric stackand exposing the first source contact portion. The method also includesforming a plurality of conductor layers through the slit opening andform a second source contact portion in the slit opening and in contactwith the first source contact portion.

In some embodiments, forming the first source contact portion includesforming a source contact pattern in the substrate and extendingcontinuously along a lateral direction and depositing a conductivematerial to fill up the source contact pattern.

In some embodiments, the method further includes planarizing theconductive material to form the first source contact portion.

In some embodiments, the method further includes depositing an adhesivelayer in the source contact pattern before the deposition of theconductive material.

In some embodiments, forming the dielectric stack includes forminginterleaved a plurality of sacrificial layers and a plurality ofdielectric layers.

In some embodiments, forming the slit opening includes forming aplurality of slit portions along the lateral direction, at least two ofthe slit portions being disconnected from each other along the lateraldirection and each exposing the first source contact portion.

In some embodiments, forming the plurality of conductor layers includesremoving the plurality of sacrificial layers through the slit opening toform a plurality of lateral recesses, and depositing a conductormaterial to fill in the lateral recesses to form the conductor layers.

In some embodiments, forming the second source contact portion includesdepositing another conductive material in the slit opening, the otherconductive material being in contact with the conductive material at aninterface coplanar with the top surface of the substrate.

In some embodiments, the method further includes depositing theconductive material above and in contact with the other conductivematerial in the slit opening.

The foregoing description of the specific embodiments will so reveal thegeneral nature of the present disclosure that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A method for forming a three-dimensional (3D)memory device, comprising: forming a first source contact portionincluding a metal in a substrate; forming a dielectric stack over thefirst source contact portion; forming a slit opening extending in thedielectric stack and exposing the first source contact portion; forminga plurality of conductor layers through the slit opening; and forming asecond source contact portion in the slit opening and in contact withthe first source contact portion.
 2. A method for forming athree-dimensional (3D) memory device, comprising: forming a first sourcecontact portion in a substrate, comprising: forming a source contactpattern in the substrate and extending continuously along a lateraldirection; and depositing a first conductive material including at leastone of tungsten, cobalt, aluminum, and copper to fill up the sourcecontact pattern; forming a dielectric stack over the first sourcecontact portion; forming a slit opening extending in the dielectricstack and exposing the first source contact portion; forming a pluralityof conductor layers through the slit opening; and forming a secondsource contact portion in the slit opening and in contact with the firstsource contact portion.
 3. The method of claim 2, further comprisingplanarizing the first conductive material to form the first sourcecontact portion.
 4. The method of claim 2, further comprising depositingan adhesive layer in the source contact pattern before the deposition ofthe first conductive material.
 5. The method of claim 2, wherein formingthe dielectric stack comprises forming interleaved a plurality ofsacrificial layers and a plurality of dielectric layers.
 6. The methodof claim 5, wherein forming the slit opening comprises forming aplurality of slit portions along the lateral direction, at least two ofthe slit portions being disconnected from each other along the lateraldirection and each exposing the first source contact portion.
 7. Themethod of claim 6, wherein forming the plurality of conductor layerscomprises: removing the plurality of sacrificial layers through the slitopening to form a plurality of lateral recesses; and depositing aconductor material to fill in the lateral recesses to form the conductorlayers.
 8. The method of claim 2, wherein forming the second sourcecontact portion comprises depositing a second conductive material in theslit opening, the second conductive material being in contact with thefirst conductive material at an interface coplanar with a top surface ofthe substrate.
 9. The method of claim 8, further comprising depositingthe first conductive material above and in contact with the secondconductive material in the slit opening.
 10. The method of claim 2,wherein forming the second source contact portion comprising forming aplurality of sub-contacts that are separated by an insulating spacer.11. A method for forming a three-dimensional (3D) memory device,comprising: forming a first source contact portion in a substrate;forming a dielectric stack over the first source contact portion;forming a slit opening extending in the dielectric stack and exposingthe first source contact portion; forming a plurality of conductorlayers through the slit opening; and form a second source contactportion in the slit opening and in contact with the first source contactportion, wherein the second source contact portion including a pluralityof sub-contacts that are separated by an insulating spacer.
 12. Themethod of claim 11, wherein forming the first source contact portioncomprises: forming a source contact pattern in the substrate andextending continuously along a lateral direction; and depositing a firstconductive material including at least one of a metal and a silicide tofill up the source contact pattern.
 13. The method of claim 12, furthercomprising planarizing the first conductive material to form the firstsource contact portion.
 14. The method of claim 12, further comprisingdepositing an adhesive layer in the source contact pattern before thedeposition of the first conductive material.
 15. The method of claim 11,wherein forming the dielectric stack comprises forming interleaved aplurality of sacrificial layers and a plurality of dielectric layers.16. The method of claim 15, wherein forming the slit opening comprisesforming a plurality of slit portions along the lateral direction, atleast two of the slit portions being disconnected from each other alongthe lateral direction and each exposing the first source contactportion.
 17. The method of claim 16, wherein forming the plurality ofconductor layers comprises: removing the plurality of sacrificial layersthrough the slit opening to form a plurality of lateral recesses; anddepositing a conductor material to fill in the lateral recesses to formthe conductor layers.
 18. The method of claim 12, wherein forming thesecond source contact portion comprises depositing a second conductivematerial in the slit opening, the second conductive material being incontact with the first conductive material at an interface coplanar witha top surface of the substrate.
 19. The method of claim 18, furthercomprising depositing the first conductive material above and in contactwith the second conductive material in the slit opening.
 20. The methodof claim 14, wherein depositing the adhesive layer comprises depositingat least one of titanium, titanium nitride, tantalum, and tantalumnitride.